This application claims the priority of German Patent Document No. 197 25 006.8, filed on Jun. 13, 1997, the disclosure of which is expressly incorporated by reference herein.
The present invention relates to a methanol reforming reactor having a reforming reaction space into which a methanol reforming catalyst is charged, as well as to a process for treating a catalyst that can be used for this purpose. Such reforming reactors are used, for example, for generating hydrogen for the fuel cells of a fuel-cell-operated motor vehicle.
Methanol reforming catalysts are known in various compositions. See, for example, German Published Patent Applications DE 33 14 131 A1 and DE 35 31 757 A1, European Published Patent Application EP 0 201 070 A2 and Japanese Published Patent Application JP 4-141234 (A). The methanol reforming catalyst is usually charged into the reforming reaction space in the form of bulk pellets.
A known fact concerning virtually all current methanol reforming catalysts is that, during the first operating hours, they experience a noticeable reduction in volume that results in a corresponding decrease of the specific activity of the catalyst material and thus of the efficiency of a methanol reforming reactor containing the catalyst.
In the case of a methanol reforming reactor of the initially mentioned type disclosed in Japanese Published Patent Application JP 63-310703 (A), the methanol reforming catalyst in the reforming reaction space is held under an applied pressure by means of a pressure-spring-loaded, movably arranged, gas-permeable cover plate. Before the start of a reforming reaction operation, a reduction reaction for the reforming catalyst situated in the reforming reaction space is carried out whose volume will then decrease. The spring-loaded cover plate compresses the catalyst material correspondingly and ensures in this manner that a dense packing of the bulk catalyst is maintained. The reduction reaction is a process required for the operation of a Cu catalyst. The decrease in volume occurring in this case is clearly lower than the decrease in volume which occurs during the normal reforming operation.
From British Published Patent Application GB 2 132 108 A, a methanol reforming reactor is known, in which for a fast start of the reactor, before the beginning of the reforming operation phase, the reforming catalyst situated in the reaction space is directly and indirectly heated in that methanol is burned in air and the combustion exhaust gas is guided through a tempering space which is in thermal contact with the reaction space as well as through the catalyst-filled reaction space itself. For the combustion operation, a stoichiometric or less than stoichiometric oxygen fraction can be selected, and, for avoiding an overheating of the catalyst, water can be sprayed into the combustion gas flow guided to the reaction space.
In German Patent Document DE 1 246 688, a methanol reforming reactor is disclosed that comprises a nickel catalyst bed and a zinc-copper catalyst bed which follows. The reforming reaction operation is periodically interrupted for catalyst treatment phases during which the catalyst system is regenerated by rinsing with a gas containing free oxygen at a raised temperature of preferably 150.degree. C. to 450.degree. and subsequently, as required, is subjected to a rinsing with a gas containing free hydrogen, in order to reactivate the nickel catalyst. The nickel catalyst is produced, for example, from a nickel salt, in which case, at the end of the production process, the final activation takes place by the reduction to metallic nickel in a hydrogen-containing or inert gas atmosphere during a treatment period of up to approximately 16 hours at a temperature of between 150.degree. C. and 600.degree. C. and a pressure of up to 14 bar. After this reduction, the nickel catalyst must no longer come in contact with air in order to prevent an oxidation of the nickel.